This research program consists essentially of (1) continuing our investigation of the etiology and mechanism of cataractogenesis in animal model systems, and (2) applying our positive findings to the study of human cataracts. Studies on biochemical and biophysical characteristics of lens proteins and their changes in the process of lens opacification have been progressing as proposed. Galactose-induced cataract in Sprague-Dawley rat has been chosen as our animal model system. The normal rat lens showed six distinctive protein fractions (F-I to F-VI) by Sephadex G-200sf gel chromatography. The cataractous lenses exhibited a gradual decrease of F-V and a relative increase in F-I as a lens became increasingly opaque. A diminution of F-II was particularly noticeable. In the severe cataractous lens, the F-II was found almost non-existent. In the study of human hypermature nuclear cataractous lens, we substantiated our previous observation that the change of soluble lens protein is similar to that in the rat model system. There seems to be a common protein pattern change in mammalian lenses during cataractogenesis. Study of rat F-II protein indicates that there is only major single polypeptide chain. It is expected that our immunological study of this protein will provide additional information concerning the characteristic of F-II and its relationship to other protein fractions. The study of the sequential changes of the proteins in neonatal and aged rat lenses have yielded information concerning the developmental aspects of the lens, from birth to senility (some cases to death). Our preliminary observations indicate that the lens protein changes due to aging in rat are not identical to those occurring in cataractogenesis.